1. Field of the Invention
This invention relates to helicopters in which in-plane vibrations of the rotor result in vibrations in the helicopter fuselage. More particularly this invention relates to improvements in bifilar absorbers connected to the helicopter rotor for rotation therewith in a plane perpendicular to the axis of rotation of the rotor.
2. Description of the Prior Art
In U.S. Pat. No. 3,540,809, issued Nov. 17, 1970 to William F. Paul et al, and assigned to the assignee of this application, a helicopter is shown equipped with bifilar absorbers. The present invention is directed to improvements in the absorbers of the Paul et al patent.
In the patent a bifilar absorber has a pendulous, or counterweight element, connected to its absorber supporting member on the rotor head by tuning pin assemblies which pass through enlarged apertures in the support member and pendulous element and include tuning pins. These tuning pins provide a rolling pendulous and vibration absorbing motion between the pendulous element and its supporting member.
In a bifilar absorber any friction between the pendulous element and its supporting member can completely destroy absorber effectiveness and to prevent face-to-face contact between the sides of the pendulous element and the adjacent sides of its support member it was necessary in the prior patent to provide washers which have tapered side walls between these confronting faces. These washers somewhat reduced the undesirable frictional damping adjacent the tuning pin in normal operation of the absorber. The present invention teaches an improved tuning pin construction which provides centering of the pendulous element of the absorber relative to its support member under the action of centrifugal force and completely eliminates face-to-face sliding contact of relatively movable absorber parts and also eliminates the need for these washers.